Generally, a hard disk drive device has a spindle motor (SPM) for rotating a disk, a head for performing disk recording and playback, an arm attached to the front end of the head, and a voice coil motor (VCM) for moving the arm. When recording or playing back data, the head is carried to the desired positions on the disk by driving with the voice coil motor.
A minute distance is maintained between the head and the disk by utilizing the flow of air arising near the surface of the rotating disk. Therefore, a hard disk drive device mounted in mobile equipment generally has a function for preventing collision between the two. For example, in cases when abnormalities in power supply voltage, environmental temperature, disk rotation speed, etc., are detected, the operation of withdrawing (retracting) the head to a safety region called a ramp is executed.
The ramp has, from the side near the disk, a rising first inclined part, a horizontal part, and a falling second inclined part. In the event of retraction, the arm is moved by the voice coil motor such that the arm rides over the first inclined part and stops in a parking area beyond the second inclined part. Because it is also necessary to perform retraction after cutting off the power supply, power supply for the voice coil motor is provided, for example, from the voltage of a pre-charged capacitor for retraction, and from the rectified voltage of the back electromotive force (BEMF) of the spindle motor from inertial rotation.    Patent Reference 1 Specification of U.S. Pat. No. 7,301,722
Incidentally, in a conventional hard disk drive device, the method for control of the voice coil motor from the starting time to the ending time of the retraction operation involves switching according to preset values of a timer. Also, in this case, it is made such that the type of power supply (voltage of capacitor/rectified voltage of BEMF) used for driving of the voice coil motor is automatically switched when the preset time arrives.
However, because the capacitor voltage is decreased by discharge, when switching of the voice coil motor power supply according to set values of the timer, the capacitor voltage may, depending on conditions, decrease to nearly zero volts by the time of switching. In such a situation, the torque of the voice coil motor may decrease temporarily, and the power to draw the arm toward the ramp side may be weakened. Then there is a possibility that, when the arm moves toward the side of the disk, it will no longer be possible to draw the arm onto the ramp.
Therefore, in the conventional hard disk drive device, it has been necessary to make the capacitance of the capacitor large enough to handle the decrease in capacitor voltage, and therefore there were the disadvantages that the circuit area was large and the component cost was high.
This invention was made taking such circumstances into consideration, and its purpose is to provide a motor control device, and a disk drive device using same, in which it is possible to supply the necessary power to the motor during emergency operation while limiting enlargement of the circuit area.